Scalable nesting of supplemental enhancement information messages in video coding

ABSTRACT

Several embodiments for video encoding and video decoding are described. An example method of processing video data includes performing a conversion between a video comprising one or more subpictures and a bitstream of the video, wherein one or more supplemental enhancement information messages that have filler payloads are processed during the conversion according to a format rule, and wherein the format rule disallows the one or more supplemental enhancement information messages having filler payloads to be in a scalable nesting supplemental enhancement information message.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/US2021/036345 filed on Jun. 08, 2021, which claims the priorityto and benefits of U.S. Provisional Pat. App. Ser. No. 63/036,743 filedon Jun. 09, 2020. All the aforementioned patent applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to image and video coding and decoding.

BACKGROUND

Digital video accounts for the largest bandwidth use on the internet andother digital communication networks. As the number of connected userdevices capable of receiving and displaying video increases, it isexpected that the bandwidth demand for digital video usage will continueto grow.

SUMMARY

The present disclosure discloses embodiments that can be used by videoencoders and decoders for processing a coded representation of a videoor an image.

In one example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising oneor more subpictures and a bitstream of the video, wherein one or moresupplemental enhancement information messages that have filler payloadsare processed during the conversion according to a format rule, andwherein the format rule disallows the one or more supplementalenhancement information messages having filler payloads to be in ascalable nesting supplemental enhancement information message.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video and a bitstreamof the video, wherein one or more syntax elements are processed duringthe conversion according to a format rule, and wherein the format rulespecifies that the one or more syntax elements are used for indicatingsubpicture information for layers of the video that have pictures withmultiple subpictures.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising aplurality of subpictures and a bitstream of the video, wherein ascalable-nested supplemental enhancement information message isprocessed during the conversion according to a format rule, and whereinthe format rule specifies use of one or more subpicture indices toassociate one or more subpictures to the scalable-nested supplementalenhancement information message.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising oneor more subpictures and a bitstream of the video according to a formatrule, wherein the format rule specifies that a first syntax element in ascalable nesting supplemental enhancement information message in thebitstream is set to a particular value in response to the scalablenesting supplemental enhancement information message including one ormore subpicture level information supplemental enhancement informationmessages, and wherein the particular value of the first syntax elementindicates that the scalable nesting supplemental enhancement informationmessage includes one or more scalable-nested supplemental enhancementinformation messages that apply to a specific output video layer set.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising aplurality of subpictures and a bitstream of the video, wherein theconversion is according to a format rule that specifies that a scalablenesting supplemental enhancement information message is disallowed fromincluding a first supplemental enhancement information message of afirst payload type and a second supplemental enhancement informationmessage of a second payload type.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video and a bitstreamof the video, wherein the conversion is performed according to a formatrule that specifies that a supplemental enhancement information networkabstraction layer unit includes a network abstraction layer unit typeequal to a prefix supplemental enhancement information networkabstraction layer unit type in response to the supplemental enhancementinformation network abstraction layer unit including a scalable nestingsupplemental enhancement information message that includes asupplemental enhancement information message not associated with aparticular payload type.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video and a bitstreamof the video, wherein the conversion is performed according to a formatrule that specifies that a supplemental enhancement information networkabstraction layer unit includes a network abstraction layer unit typeequal to a suffix supplemental enhancement information networkabstraction layer unit type in response to the supplemental enhancementinformation network abstraction layer unit including a scalable nestingsupplemental enhancement information message that includes asupplemental enhancement information message associated with aparticular payload type.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising oneor more subpictures or one or more subpicture sequences and a codedrepresentation of the video, wherein the coded representation conformsto a format rule specifying whether or how scalable-nested supplementalenhancement information (SEI) is included in the coded representation.

In yet another example aspect, a video encoder apparatus is disclosed.The video encoder comprises a processor configured to implementabove-described methods.

In yet another example aspect, a video decoder apparatus is disclosed.The video decoder comprises a processor configured to implementabove-described methods.

In yet another example aspect, a computer readable medium having codestored thereon is disclosed. The code embodies one of the methodsdescribed herein in the form of processor-executable code.

These, and other, features are described throughout the presentdisclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of raster-scan slice partitioning of a picture,where the picture is divided into 12 tiles and 3 raster-scan slices.

FIG. 2 shows an example of rectangular slice partitioning of a picture,where the picture is divided into 24 tiles (6 tile columns and 4 tilerows) and 9 rectangular slices.

FIG. 3 shows an example of a picture partitioned into tiles andrectangular slices, where the picture is divided into 4 tiles (2 tilecolumns and 2 tile rows) and 4 rectangular slices.

FIG. 4 shows a picture that is partitioned into 15 tiles, 24 slices, and24 subpictures.

FIG. 5 is a block diagram of an example video processing system.

FIG. 6 is a block diagram of a video processing apparatus.

FIG. 7 is a flowchart for an example method of video processing.

FIG. 8 is a block diagram that illustrates a video coding system inaccordance with some embodiments of the present disclosure.

FIG. 9 is a block diagram that illustrates an encoder in accordance withsome embodiments of the present disclosure.

FIG. 10 is a block diagram that illustrates a decoder in accordance withsome embodiments of the present disclosure.

FIG. 11 shows an example of a typical subpicture-basedviewport-dependent 360° video coding scheme.

FIG. 12 shows a viewport-dependent 360° video coding scheme based onsubpictures and spatial scalability.

FIGS. 13 to 19 are flowcharts for example methods of processing videodata.

DETAILED DESCRIPTION

Section headings are used in the present disclosure for ease ofunderstanding and do not limit the applicability of embodimentsdisclosed in each section only to that section. Furthermore, H.266terminology is used in some description only for ease of understandingand not for limiting scope of the disclosed embodiments. As such, theembodiments described herein are applicable to other video codecprotocols and designs also. In the present disclosure, editing changesare shown to text with double square brackets enclosing cancelled text,and highlight (e.g., boldface italics) indicating added text, withrespect to the current draft of the versatile video coding (VVC)specification.

1. Introduction

This disclosure is related to video coding technologies. Specifically,it is about specifying and signalling level information for subpicturesequences. It may be applied to any video coding standard ornon-standard video codec that supports single-layer video coding andmulti-layer video coding, e.g., VVC that is being developed.

2. Abbreviations

APS Adaptation Parameter Set

AU Access Unit

AUD Access Unit Delimiter

AVC Advanced Video Coding

BP Buffering Period

CLVS Coded Layer Video Sequence

CPB Coded Picture Buffer

CRA Clean Random Access

CTU Coding Tree Unit

CVS Coded Video Sequence

DPB Decoded Picture Buffer

DPS Decoding Parameter Set

DUI Decoding Unit Information

EOB End Of Bitstream

EOS End Of Sequence

GCI General Constraints Information

GDR Gradual Decoding Refresh

HEVC High Efficiency Video Coding

HRD Hypothetical Reference Decoder

IDR Instantaneous Decoding Refresh

TRAP Intra Random Access Points

JEM Joint Exploration Model

MCTS Motion-Constrained Tile Sets

NAL Network Abstraction Layer

OLS Output Layer Set

PH Picture Header

PPS Picture Parameter Set

PT Picture Timing

PTL Profile, Tier and Level

PU Picture Unit

RRP Reference Picture Resampling

RBSP Raw Byte Sequence Payload

SEI Supplemental Enhancement Information

SH Slice Header

SLI Subpicture Level Information

SPS Sequence Parameter Set

SVC Scalable Video Coding

VCL Video Coding Layer

VPS Video Parameter Set

VTM VVC Test Model

VUI Video Usability Information

VVC Versatile Video Coding

3. Initial discussion

Video coding standards have evolved primarily through the development ofthe well-known International Telecommunication Union (ITU)Telecommunication Standardization Sector (ITU-T) and InternationalOrganization for Standardization (ISO)/International ElectrotechnicalCommission (IEC) standards. The ITU-T produced H.261 and H.263, ISO/IECproduced Moving Picture Experts Group (MPEG)-1 and MPEG-4 Visual, andthe two organizations jointly produced the H.262/MPEG-2 Video andH.264MPEG-4 Advanced Video Coding (AVC) and H.265HEVC standards. SinceH.262, the video coding standards are based on the hybrid video codingstructure wherein temporal prediction plus transform coding areutilized. To explore the future video coding technologies beyond HEVC,the Joint Video Exploration Team (WET) was founded by Video CodingExperts Group (VCEG) and MPEG jointly in 2015. Since then, many newmethods have been adopted by JVET and put into the reference softwarenamed Joint Exploration Model (JEM). The JVET meeting is concurrentlyheld once every quarter, and the new coding standard is targeting a 50%bitrate reduction as compared to HEVC. The new video coding standard wasofficially named as Versatile Video Coding (VVC) in the April 2018 JVETmeeting, and the first version of VVC test model (VTM) was released atthat time. As there are continuous effort contributing to VVCstandardization, new coding techniques are being adopted to the VVCstandard in every JVET meeting. The VVC working draft and test model VTMare then updated after every meeting. The VVC project is now aiming fortechnical completion (FDIS) at the July 2020 meeting.

3.1. Picture Partitioning Schemes in HEVC

HEVC includes four different picture partitioning schemes, namelyregular slices, dependent slices, tiles, and wavefront parallelprocessing (WPP), which may be applied for maximum transfer unit (MTU)size matching, parallel processing, and reduced end-to-end delay.

Regular slices are similar as in H.264AVC. Each regular slice isencapsulated in its own NAL unit, and in-picture prediction (intrasample prediction, motion information prediction, coding modeprediction) and entropy coding dependency across slice boundaries aredisabled. Thus, a regular slice can be reconstructed independently fromother regular slices within the same picture (though there may stillhave interdependencies due to loop filtering operations).

The regular slice is the only tool that can be used for parallelizationthat is also available, in virtually identical form, in H.264AVC.Regular slice-based parallelization does not require muchinter-processor or inter-core communication (except for inter-processoror inter-core data sharing for motion compensation when decoding apredictively coded picture, which is typically much heavier thaninter-processor or inter-core data sharing due to in-pictureprediction). However, for the same reason, the use of regular slices canincur substantial coding overhead due to the bit cost of the sliceheader and due to the lack of prediction across the slice boundaries.Further, regular slices (in contrast to the other tools mentioned below)also serve as the key mechanism for bitstream partitioning to match MTUsize requirements, due to the in-picture independence of regular slicesand that each regular slice is encapsulated in its own NAL unit. In manycases, the goal of parallelization and the goal of MTU size matchingplace contradicting demands to the slice layout in a picture. Therealization of this situation led to the development of theparallelization tools mentioned below.

Dependent slices have short slice headers and allow partitioning of thebitstream at treeblock boundaries without breaking any in-pictureprediction. Basically, dependent slices provide fragmentation of regularslices into multiple NAL units, to provide reduced end-to-end delay byallowing a part of a regular slice to be sent out before the encoding ofthe entire regular slice is finished.

In WPP, the picture is partitioned into single rows of coding treeblocks (CTBs). Entropy decoding and prediction are allowed to use datafrom CTBs in other partitions. Parallel processing is possible throughparallel decoding of CTB rows, where the start of the decoding of a CTBrow is delayed by two CTBs, so to ensure that data related to a CTBabove and to the right of the subject CTB is available before thesubject CTB is being decoded. Using this staggered start (which appearslike a wavefront when represented graphically), parallelization ispossible with up to as many processors/cores as the picture contains CTBrows. Because in-picture prediction between neighboring treeblock rowswithin a picture is permitted, the required inter-processor/inter-corecommunication to enable in-picture prediction can be substantial. TheWPP partitioning does not result in the production of additional NALunits compared to when it is not applied, thus WPP is not a tool for MTUsize matching. However, if MTU size matching is required, regular slicescan be used with WPP, with certain coding overhead.

Tiles define horizontal and vertical boundaries that partition a pictureinto tile columns and rows. Tile column runs from the top of a pictureto the bottom of the picture. Likewise, tile row runs from the left ofthe picture to the right of the picture. The number of tiles in apicture can be derived simply as number of tile columns multiplied bynumber of tile rows.

The scan order of CTBs is changed to be local within a tile (in theorder of a CTB raster scan of a tile), before decoding the top-left CTBof the next tile in the order of tile raster scan of a picture. Similarto regular slices, tiles break in-picture prediction dependencies aswell as entropy decoding dependencies. However, they do not need to beincluded into individual NAL units (same as WPP in this regard); hence,tiles cannot be used for MTU size matching. Each tile can be processedby one processor/core, and the inter-processor/inter-core communicationrequired for in-picture prediction between processing units decodingneighboring tiles is limited to conveying the shared slice header incases a slice is spanning more than one tile, and loop filtering relatedsharing of reconstructed samples and metadata. When more than one tileor WPP segment is included in a slice, the entry point byte offset foreach tile or WPP segment other than the first one in the slice issignalled in the slice header.

For simplicity, restrictions on the application of the four differentpicture partitioning schemes have been specified in HEVC. A given codedvideo sequence cannot include both tiles and wavefronts for most of theprofiles specified in HEVC. For each slice and tile, either or both ofthe following conditions must be fulfilled: 1) all coded treeblocks in aslice belong to the same tile; 2) all coded treeblocks in a tile belongto the same slice. Finally, a wavefront segment contains exactly one CTBrow, and when WPP is in use, if a slice starts within a CTB row, it mustend in the same CTB row.

A recent amendment to HEVC is specified in the JCT-VC output documentJCTVC-AC1005, J. Boyce, A. Ramasubramonian, R. Skupin, G. J. Sullivan,A. Tourapis, Y.-K. Wang (editors), “HEVC Additional SupplementalEnhancement Information (Draft 4),” Oct. 24, 2017, publicly availableherein:http://phenix.int-evry.fr/jct/doc_end_user/documents/29_Macau/wg11/JCTVC-AC1005-v2.zip.With this amendment included, HEVC specifies three MCTS-related SEImessages, namely temporal MCTSs SEI message, MCTSs extractioninformation set SEI message, and MCTSs extraction information nestingSEI message.

The temporal MCTSs SEI message indicates existence of MCTSs in thebitstream and signals the MCTSs. For each MCTS, motion vectors arerestricted to point to full-sample locations inside the MCTS and tofractional-sample locations that require only full-sample locationsinside the MCTS for interpolation, and the usage of motion vectorcandidates for temporal motion vector prediction derived from blocksoutside the MCTS is disallowed. This way, each MCTS may be independentlydecoded without the existence of tiles not included in the MCTS.

The MCTSs extraction information sets SEI message provides supplementalinformation that can be used in the MCTS sub-bitstream extraction(specified as part of the semantics of the SEI message) to generate aconforming bitstream for an MCTS set. The information consists of anumber of extraction information sets, each defining a number of MCTSsets and containing RBSP bytes of the replacement VPSs, SPSs, and PPSsto be used during the MCTS sub-bitstream extraction process. Whenextracting a sub-bitstream according to the MCTS sub-bitstreamextraction process, parameter sets (VPSs, SPSs, and PPSs) need to berewritten or replaced, slice headers need to be slightly updated becauseone or all of the slice address related syntax elements (including firstslice segment in_pic flag and slice segment_address) typically wouldneed to have different values.

3.2. Partitioning of Pictures in VVC

In VVC, a picture is divided into one or more tile rows and one or moretile columns. A tile is a sequence of CTUs that covers a rectangularregion of a picture. The CTUs in a tile are scanned in raster scan orderwithin that tile.

A slice consists of an integer number of complete tiles or an integernumber of consecutive complete CTU rows within a tile of a picture.

Two modes of slices are supported, namely the raster-scan slice mode andthe rectangular slice mode. In the raster-scan slice mode, a slicecontains a sequence of complete tiles in a tile raster scan of apicture. In the rectangular slice mode, a slice contains either a numberof complete tiles that collectively form a rectangular region of thepicture or a number of consecutive complete CTU rows of one tile thatcollectively form a rectangular region of the picture. Tiles within arectangular slice are scanned in tile raster scan order within therectangular region corresponding to that slice.

A subpicture contains one or more slices that collectively cover arectangular region of a picture.

FIG. 1 shows an example of raster-scan slice partitioning of a picture,where the picture is divided into 12 tiles and 3 raster-scan slices.

FIG. 2 shows an example of rectangular slice partitioning of a picture,where the picture is divided into 24 tiles (6 tile columns and 4 tilerows) and 9 rectangular slices.

FIG. 3 shows an example of a picture partitioned into tiles andrectangular slices, where the picture is divided into 4 tiles (2 tilecolumns and 2 tile rows) and 4 rectangular slices.

FIG. 4 shows an example of subpicture partitioning of a picture, where apicture is partitioned into 18 tiles: 12 on the left-hand side, eachcovering one slice of 4-by-4 CTUs; and 6 tiles on the right-hand side,each covering 2 vertically-stacked slices of 2-by-2 CTUs, altogetherresulting in 24 slices and 24 subpictures of varying dimensions (eachslice is a subpicture).

3.3. Picture Resolution Change within a Sequence

In AVC and HEVC, the spatial resolution of pictures cannot change unlessa new sequence using a new SPS starts, with an IRAP picture. VVC enablespicture resolution change within a sequence at a position withoutencoding an IRAP picture, which is always intra-coded. This feature issometimes referred to as reference picture resampling (RPR), as thefeature needs resampling of a reference picture used for interprediction when that reference picture has a different resolution thanthe current picture being decoded.

The scaling ratio is restricted to be greater than or equal to 1/2 (2times downsampling from the reference picture to the current picture),and less than or equal to 8 (8 times upsampling). Three sets ofresampling filters with different frequency cutoffs are specified tohandle various scaling ratios between a reference picture and thecurrent picture. The three sets of resampling filters are appliedrespectively for the scaling ratio ranging from 1/2 to 1/1.75, from1/1.75 to 1/1.25, and from 1/1.25 to 8. Each set of resampling filtershas 16 phases for luma and 32 phases for chroma which is same to thecase of motion compensation interpolation filters. Actually, the normalMC interpolation process is a special case of the resampling processwith scaling ratio ranging from 1/1.25 to 8. The horizontal and verticalscaling ratios are derived based on picture width and height, and theleft, right, top and bottom scaling offsets specified for the referencepicture and the current picture.

Other aspects of the VVC design for support of this feature that aredifferent from HEVC include: i) the picture resolution and thecorresponding conformance window are signalled in the PPS instead of inthe SPS, while in the SPS the maximum picture resolution is signalled;and ii) for a single-layer bitstream, each picture store (a slot in theDPB for storage of one decoded picture) occupies the buffer size asrequired for storing a decoded picture having the maximum pictureresolution.

3.4. Scalable Video Coding (SVC) in General and in VVC

Scalable video coding (SVC, sometimes also referred to as scalability invideo coding) refers to video coding in which a base layer (BL),sometimes referred to as a reference layer (RL), and one or morescalable enhancement layers (ELs) are used. In SVC, the base layer cancarry video data with a base level of quality. The one or moreenhancement layers can carry additional video data to support, forexample, higher spatial, temporal, and/or signal-to-noise (SNR) levels.Enhancement layers may be defined relative to a previously encodedlayer. For example, a bottom layer may serve as a BL, while a top layermay serve as an EL. Middle layers may serve as either ELs or RLs, orboth. For example, a middle layer (e.g., a layer that is neither thelowest layer nor the highest layer) may be an EL for the layers belowthe middle layer, such as the base layer or any intervening enhancementlayers, and at the same time serve as a RL for one or more enhancementlayers above the middle layer. Similarly, in the multiview orthree-dimensional (3D) extension of the HEVC standard, there may bemultiple views, and information of one view may be utilized to code(e.g., encode or decode) the information of another view (e.g., motionestimation, motion vector prediction and/or other redundancies).

In SVC, the parameters used by the encoder or the decoder are groupedinto parameter sets based on the coding level (e.g., video-level,sequence-level, picture-level, slice level, etc.) in which they may beutilized. For example, parameters that may be utilized by one or morecoded video sequences of different layers in the bitstream may beincluded in a video parameter set (VPS), and parameters that areutilized by one or more pictures in a coded video sequence may beincluded in a sequence parameter set (SPS). Similarly, parameters thatare utilized by one or more slices in a picture may be included in apicture parameter set (PPS), and other parameters that are specific to asingle slice may be included in a slice header. Similarly, theindication of which parameter set(s) a particular layer is using at agiven time may be provided at various coding levels.

Thanks to the support of reference picture resampling (RPR) in VVC,support of a bitstream containing multiple layers, e.g., two layers withstandard definition (SD) and high definition (HD) resolutions in VVC canbe designed without the need any additional signal-processing-levelcoding tool, as upsampling needed for spatial scalability support canjust use the RPR upsampling filter. Nevertheless, high-level syntaxchanges (compared to not supporting scalability) are needed forscalability support. Scalability support is specified in VVC version 1.Different from the scalability supports in any earlier video codingstandards, including in extensions of AVC and HEVC, the design of VVCscalability has been made friendly to single-layer decoder designs asmuch as possible. The decoding capability for multi-layer bitstreams arespecified in a manner as if there were only a single layer in thebitstream. For example, the decoding capability, such as DPB size, isspecified in a manner that is independent of the number of layers in thebitstream to be decoded. Basically, a decoder designed for single-layerbitstreams does not need much change to be able to decode multi-layerbitstreams. Compared to the designs of multi-layer extensions of AVC andHEVC, the hypertext transfer protocol live streaming (HLS) aspects havebeen significantly simplified at the sacrifice of some flexibilities.For example, an TRAP AU is required to contain a picture for each of thelayers present in the CVS.

3.5. Viewport-dependent 360° Video Streaming Based on Subpictures

In streaming of 360° video (also referred to as omnidirectional video),at any particular moment only a subset (i.e., the current viewport) ofthe entire omnidirectional video sphere would be rendered to the user,while the user can turn his/her head anytime to change the viewingorientation and consequently the current viewport. While it is desirableto have at least some lower-quality representation of the area notcovered by the current viewport available at the client and ready to berendered to the user just in case the user suddenly changes his/herviewing orientation to anywhere on the sphere, a high-qualityrepresentation of the omnidirectional video is only needed for thecurrent viewport that is being rendered to the use right now. Splittingthe high-quality representation of the entire omnidirectional video intosubpictures at an appropriate granularity enables such an optimization.Using VVC, the two representations can be encoded as two layers that areindependent from each other.

A typical subpicture-based viewport-dependent 360° video delivery schemeis shown in FIG. 11 , wherein a higher-resolution representation of thefull video consists of subpictures, while a lower-resolutionrepresentation of the full video does not use subpictures and can becoded with less frequent random access points than the higher-resolutionrepresentation. The client receives the full video in thelower-resolution and for the higher-resolution video the client onlyreceives and decodes the subpictures that cover the current viewport.

The latest VVC draft specification also supports the improved 360° videocoding scheme as shown in FIG. 12 . The only difference compared to theapproach shown in FIG. 11 is that inter-layer prediction (ILP) isapplied for the approach shown in FIG. 12 .

3.6. Parameter Sets

AVC, HEVC, and VVC specify parameter sets. The types of parameter setsinclude SPS, PPS, APS, and VPS. SPS and PPS are supported in all of AVC,HEVC, and VVC. VPS was introduced since HEVC and is included in bothHEVC and VVC. APS was not included in AVC or HEVC but is included in thelatest VVC draft text.

SPS was designed to carry sequence-level header information, and PPS wasdesigned to carry infrequently changing picture-level headerinformation. With SPS and PPS, infrequently changing information neednot to be repeated for each sequence or picture, hence redundantsignalling of this information can be avoided. Furthermore, the use ofSPS and PPS enables out-of-band transmission of the important headerinformation, thus not only avoiding the need for redundant transmissionsbut also improving error resilience.

VPS was introduced for carrying sequence-level header information thatis common for all layers in multi-layer bitstreams.

APS was introduced for carrying such picture-level or slice-levelinformation that needs quite some bits to code, can be shared bymultiple pictures, and in a sequence there can be quite many differentvariations.

3.7. Specifying and Signalling of Nested SEI Messages for SubpictureSequences in VVC

In the latest VVC draft text, the specifying and signalling of nestedSEI messages subpicture sequences in VVC are through the scalablenesting SEI message. A subpicture sequence is defined in the semanticsof the subpicture level information (SLI) SEI message. A subpicturesequence can be extracted from a bitstream by applying the subpicturesub-bitstream extraction process specified in clause C.7 of VVC.

The syntax and semantics of the scalable nesting SEI message in thelatest VVC draft text are as follows.

D.6.1 Scalable Nesting SEI Message Syntax

Descriptor scalable_nesting( payloadSize ) {  sn_ols_flag u(1) sn_subpic_flag u(1)  if( sn_ols_flag ) {   sn_num_olss_minus1 ue(v)  for( i = 0; i <= sn_num_olss_minus1; i++ )    sn_ols_idx_delta_minus1[i ] ue(v)  } else {   sn_all_layers_flag u(1)   if( !sn_all_layers_flag) {    sn_num_layers_minus1 ue(v)    for( i = 1; i <=sn_num_layers_minus1; i++ )     sn_layer_id[ i ] u(6)   }  }  if(sn_subpic_flag ) {   sn_num_subpics_minus1 ue(v)  sn_subpic_id_len_minus1 ue(v)   for( i = 0; i <=sn_num_subpics_minus1; i++ )    sn_subpic_id[ i ] u(v)  } sn_num_seis_minus1 ue(v)  while( !byte_aligned( ) )   sn_zero_bit /*equal to 0 */ u(1)  for( i = 0; i <= sn_num_seis_minus1; i++ )  sei_message( ) }

D.6.2 Scalable Nesting SEI Message Semantics

The scalable nesting SEI message provides a mechanism to associate SEImessages with specific OLSs or with specific layers and also associateSEI messages with specific sets of subpictures. A scalable nesting SEImessage contains one or more SEI messages. The SEI messages contained inthe scalable nesting SEI message are also referred to as thescalable-nested SEI messages. It is a requirement of bitstreamconformance that the following restrictions apply on containing of SEImessages in a scalable nesting SEI message:

-   An SEI message that has payloadType equal to 132 (decoded picture    hash) shall only be contained in a scalable nesting SEI message with    sn_subpic_flag equal to 1.-   An SEI message that has payloadType equal to 133 (scalable nesting)    shall not be contained in a scalable nesting SEI message.-   When a scalable nesting SEI message contains a BP, PT, or DUI SEI    message, the scalable nesting SEI message shall not contain any    other SEI message with payloadType not equal to 0 (BP), 1 (PT), or    130 (DUI).    It is a requirement of bitstream conformance that the following    restriction applies on the value of the nal_unit_type of the SEI NAL    unit containing a scalable nesting SEI message:-   When a scalable nesting SEI message contains an SEI message that has    payloadType equal to 0 (BP), 1 (PT), 130 (DUI), 145 (DRAP    indication), or 168 (frame-field information), the SEI NAL unit    containing the scalable nesting SEI message shall have nal_unit_type    equal to PREFIX_SEI_NUT.    sn_ols_flag equal to 1 specifies that the scalable-nested SEI    messages apply to specific OLSs. sn_ols_flag equal to 0 specifies    that the scalable-nested SEI messages apply to specific layers. It    is a requirement of bitstream conformance that the following    restrictions apply on the value of sn_ols_flag:-   When the scalable nesting SEI message contains an SEI message that    has payloadType equal to 0 (BP), 1 (PT), or 130 (DUI), the value of    sn_ols_flag shall be equal to 1.-   When the scalable nesting SEI message contains an SEI message that    has payloadType equal to a value in VclAssociatedSeiList, the value    of sn_ols_flag shall be equal to 0.    sn_subpic_flag equal to 1 specifies that the scalable-nested SEI    messages that apply to specified OLSs or layers apply only to    specific subpictures of the specified OLSs or layers. sn_subpic_flag    equal to 0 specifies that the scalable-nested SEI messages that    apply to specific OLSs or layers apply to all subpictures of the    specified OLSs or layers.    sn_num_olss_minus1 plus 1 specifies the number of OLSs to which the    scalable-nested SEI messages apply. The value of sn_num_olss minus1    shall be in the range of 0 to TotalNumOlss−1, inclusive.    sn_ols_idx_delta_minus1[i] is used to derive the variable    NestingOlsIdx[i] that specifies the OLS index of the i-th OLS to    which the scalable-nested SEI messages apply when sn _ols_flag is    equal to 1. The value of sn_ols_idx_delta_minus1[i] shall be in the    range of 0 to TotalNumOlss−2, inclusive, inclusive.    The variable NestingOlsIdx[i] is derived as follows:

if( i = = 0 )  NestingOlsIdx[ i ] = sn_ols_idx_delta_minus1[ i ] (D.4)else  NestingOlsIdx[ i ] = NestingOlsIdx[ i − 1 ] + sn_ols_idx_delta_minus1[ i ] + 1sn_all_layers_flag equal to 1 specifies that the scalable-nested SEImessages apply to all layers that have nuh_layer_id greater than orequal to the nuh layer id of the current SEI NAL unit.sn_all_layers_flag equal to 0 specifies that the scalable-nested SEImessages may or may not apply to all layers that have nuh_layer_idgreater than or equal to the nuh_layer_id of the current SEI NAL unit.sn_num_layers_minus1 plus 1 specifies the number of layers to which thescalable-nested SEI messages apply. The value of sn_num_layers_minus1shall be in the range of 0 tovps_max_layers_minus1−GeneralLayerIdx[nuh_layer_id], inclusive, wherenuh_layer_id is the nuh_layer_id of the current SEI NAL unit.sn_layer_id[i] specifies the nuh_layer_id value of the i-th layer towhich the scalable-nested SEI messages apply when sn_all_layers_flag isequal to 0. The value of sn_layer_id[i] shall be greater thannuh_layer_id, where nuh_layer id is the nuh_layer_id of the current SEINAL unit.When sn_ols_flag is equal to 0, the variable nestingNumLayers,specifying the nubmer of layer to which the scalable-nested SEI messagesapply, and the list nestingLayerId[i] for i in the range of 0 tonestingNumLayers−1, inclusive, specifying the list of nuh_layer_id valueof the layers to which the scalable-nested SEI messages apply, arederived as follows, where nuh_layer_id is the nuh_layer_id of thecurrent SEI NAL unit:

if( sn_all_layers_flag ) {  nestingNumLayers = vps_max_layers_minus1 + 1− GeneralLayerIdx[ nuh_layer_id ]  for( i = 0; i < nestingNumLayers; i++ )   nestingLayerId[ i ] = vps_layer_id[ GeneralLayerIdx[  nuh_layer_id ] + i ]  (D.5) } else {  nestingNumLayers =sn_num_layers_minus1 + 1  for( i = 0; i < nestingNumLayers; i ++)  nestingLayerId[ i ] = ( i = = 0 ) ? nuh_layer_id : sn_layer_id[ i ] }sn_num_subpics_minus1 plus 1 specifies the number of subpictures towhich the scalable-nested SEI messages apply. The value ofsn_num_subpics minus1 shall be less than or equal to the value ofsps_num_subpics_minus1 in the SPS referred to by the pictures in theCLVS.sn_subpic_id_len_minus1 plus 1 specifies the number of bits used torepresent the syntax element sn_subpic_id[i]. The value ofsn_subpic_id_len_minus1 shall be in the range of 0 to 15, inclusive. Itis a requirement of bitstream conformance that the value ofsn_subpic_id_len_minus1 shall be the same for all scalable nesting SEImessages that are present in a CLVS.sn_subpic_id[i] indicates the i-th subpicture ID associated with thescalable-nested SEI messages. The length of the sn_subpic_id[i] syntaxelement is sn_subpic_id_len_minus1+1 bits.sn_num_seis_minus1 plus 1 specifies the number of scalable-nested SEImessages. The value of sn_ num_seis_minus1 shall be in the range of 0 to63, inclusive.sn_zero_bit shall be equal to 0.

4. Technical Problems Solved By Disclosed Technical Solutions

The existing VVC design for specifying and signalling of nested SEImessages for subpictures and subpicture sequences, through the scalablenesting SEI message, has the following problems:

-   1) For associating a scalable-nested SEI message to one or more    subpictures, the scalable nesting SEI message uses subpicture IDs.    However, the persistency scope of a scalable-nested SEI message can    be a number of consecutive AUs, while the subpicture ID of the    subpictures with a particular subpicture index in a layer can change    within a CLVS. Therefore, instead of using subpicture IDs,    subpicture indices should be used in the scalable nesting SEI    message.-   2) Filler payload SEI messages, when present, need to be removed    from the output bitstream in the subpicture sub-bitstream extraction    process when the associated subpictures are removed. However, when    it is possible to include filler payload SEI messages in a scalable    nesting SEI message, the removal of filler payload SEI messages in    the subpicture sub-bitstream extraction process would sometimes need    to extract some scalable-nested SEI messages from a scalable nesting    SEI message.-   3) Since the SLI SEI message applies to OLSs, like the other three    HRD related SEI messages (i.e., the BP/PT/DUI SEI messages), when    SLI SEI messages are scalable-nested, the value of sn_ols_flag need    to be equal to 1. Furthermore, since the SLI SEI message specifies    information for all subpictures in the pictures in the OLSs to which    the SLI SEI message applies, it does not make sense for the value of    sn_subpic_flag to be equal to 1 for a scalable nesting SEI message    containing SLI SEI messages.-   4) There lacks a constraint to require that when a scalable nesting    SEI message contains a BP, PT, DUI, or SLI SEI message, the scalable    nesting SEI message shall not contain any other SEI message with    payloadType not equal to 0 (BP), 1 (PT), 130 (DUI), or 203 (SLI).-   5) It is specified that when a scalable nesting SEI message contains    an SEI message that has payloadType equal to 0 (BP), 1 (PT), 130    (DUI), 145 (DRAP indication), or 168 (frame-field information), the    SEI NAL unit containing the scalable nesting SEI message shall have    nal_unit_type equal to PREFIX_SEI_NUT. However, when nesting many    other SEI messages, the value of the scalable nesting SEI message    shall also have nal_unit_type equal to PREFIX_SEI_NUT.-   6) There lacks a constraint that, when a scalable nesting SEI    message contains an SEI message that has payloadType equal to 132    (decoded picture harsh), the SEI NAL unit containing the scalable    nesting SEI message shall have nal_unit_type equal to    SUFFIX_SEI_NUT.

7) The semantics of sn_num_subpics_minus1 and sn_subpic_idx[i] need tobe specified in a way such that the syntax elements are about thesubpictures of the layers with multiple subpictures per picture, to beable to support cases wherein an OLS has some layers with multiplesubpictures per picture and some other layers with a single subpictureper picture.

5. A listing of Solutions and Embodiments

To solve the above problems, and others, methods as summarized below aredisclosed. The solution items should be considered as examples toexplain the general concepts and should not be interpreted in a narrowway. Furthermore, these items can be applied individually or combined inany manner.

-   1) To solve the 1st problem, use subpicture indices (instead of    using subpicture IDs) for associating subpictures to scalable-nested    SEI messages in the scalable nesting SEI message.    -   a. In one example, change the syntax element sn_subpic_id[i] to        sn_subpic_idx[i], and consequently, remove the        sn_subpic_id_len_minus1 syntax element.-   2) To solve the 2nd problem, it is prohibited for filler payload SEI    messages to be scalable-nested, i.e., contained in a scalable    nesting SEI message.-   3) To solve the 3rd problem, add a constraint such that, when a    scalable nesting SEI message contains one or more SLI SEI messages,    the value of sn_ols_flag shall be equal to 1.    -   a. In one example, furthermore, or alternatively, add a        constraint such that, when a scalable nesting SEI message        contains one or more SLI SEI messages, the value of        sn_subpic_flag shall be equal to 0.-   4) To solve the 4^(th) problem, it is required that, that when a    scalable nesting SEI message contains a BP, PT, DUI, or SLI SEI    message, the scalable nesting SEI message shall not contain any    other SEI message with payloadType not equal to 0 (BP), 1 (PT), 130    (DUI), or 203 (SLI).-   5) To solve the 5^(th) problem, it is specified that when a scalable    nesting SEI message contains an

SEI message that has payloadType not equal to 3 (filler payload) or 132(decoded picture hash), the SEI NAL unit containing the scalable nestingSEI message shall have nal_unit_type equal to PREFIX_SEI_NUT.

-   6) To solve the 6th problem, add a constraint such that when a    scalable nesting SEI message contains an SEI message that has    payloadType equal to 132 (decoded picture hash), the SEI NAL unit    containing the scalable nesting SEI message shall have nal_unit_type    equal to SUFFIX_SEI_NUT.-   7) To solve the 7th problem, the semantics of sn_num_subpics minus1    and sn_subpic_idx[i] are specified in a way such that the syntax    elements specify information about the subpictures of the layers    that have multiple subpictures per picture.

6. Embodiments

Below are some example embodiments for some of the invention aspectssummarized above in this Section, which can be applied to the VVCspecification. The changed texts are based on the latest VVC text inJVET-S0152-v5. Most relevant parts that have been added or modified areindicated in

text, and some of the deleted parts are marked by open and close doublesquare brackets (e.g., [[]]) with deleted text in between the doublebrackets.

6.1. Embodiment 1

This embodiment is for items 1 to 5 and some of their sub-items.

D.6.1 Scalable Nesting SEI Message Syntax

Descriptor scalable_nesting( payloadSize ) { sn_ols_flag u(1)sn_subpic_flag u(1) f( sn_ols_flag ) {  sn_num_olss_minus1 ue(v)  for( i= 0; i <= sn_num_olss_minus1; i++ )   sn_ols_idx_delta_minus1[ i ] ue(v)} else {  sn_all_layers_flag u(1)  if( ! sn_all_layers_flag ) {  sn_num_layers_minus1 ue(v)   for( i = 1; i <= sn_num_layers_minus1;i++ )    sn_layer_id[ i ] u(6)  } } if( sn_subpic_flag ) { sn_num_subpics_minus1 ue(v) [[  sn_subpic_id_len_minus1]] [[ue(v)]] for( i = 0; i <= sn_num_subpics_minus1; i++ )   sn_subpic_idx[ i ]ue(v) } sn_num_seis_minus1 ue(v) while( !byte_aligned( ) )  sn_zero_bit/* equal to 0 */ u(1) for( i = 0; i <= sn_num_seis_minus1; i++ ) sei_message( ) }

D.6.2 Scalable Nesting SEI Message Semantics

The scalable nesting SEI message provides a mechanism to associate SEImessages with specific OLSs or with specific layers as well as toassociate SEI messages with specific sets of subpictures. A scalablenesting SEI message contains one or more SEI messages. The SEI messagescontained in the scalable nesting SEI message are also referred to asthe scalable-nested SEI messages.It is a requirement of bitstream conformance that the followingrestrictions apply on containing of SEI messages in a scalable nestingSEI message:

-   [[An SEI message that has payloadType equal to 132 (decoded picture    hash) shall only be contained in a scalable nesting SEI message with    sn_subpic_flag equal to 1.]]-   An SEI message that has payloadType equal to    133 (scalable nesting) shall not be contained in a scalable nesting    SEI message.-   When a scalable nesting SEI message contains a BP, PT, [[or]] DUI,    SEI message, the scalable nesting SEI message shall not contain any    other SEI message with payloadType not equal to 0 (BP), 1    (PT),[[or]] 130 (DUI),    It is a requirement of bitstream conformance that the following    restriction applies on the value of the nal_unit_type of the SEI NAL    unit containing a scalable nesting SEI message:-   When a scalable nesting SEI message contains an SEI message that has    payloadType    [[equal to 0 (BP), 1 (PT), 130 (DUI), 145 (DRAP indication), or 168    (frame-field information)]], the SEI NAL unit containing the    scalable nesting SEI message shall have nal_unit type equal to    PREFIX_SEI NUT.-       sn_ols_flag equal to 1 specifies that the scalable-nested SEI    messages apply to specific OLSs. sn_ols_flag equal to 0 specifies    that the scalable-nested SEI messages apply to specific layers.    It is a requirement of bitstream conformance that the following    restrictions apply on the value of sn_ols_flag:-   When the scalable nesting SEI message contains an SEI message that    has payloadType equal to 0 (BP), 1 (PT), [[or]] 130 (DUI),    , (SLI), the value of sn_ols_flag shall be equal to 1.-   When the scalable nesting SEI message contains an SEI message that    has payloadType equal to a value in NestingForLayersSeiList    , the value of sn_ols_flag shall be equal to 0.    sn_subpic_flag equal to 1 specifies that the scalable-nested SEI    messages that apply to specified OLSs or layers apply only to    specific subpictures of the specified OLSs or layers. sn_subpic_flag    equal to 0 specifies that the scalable-nested SEI messages that    apply to specific OLSs or layers apply to all subpictures of the    specified OLSs or layers.    sn_num_olss_minus1 plus 1 specifies the number of OLSs to which the    scalable-nested SEI messages apply. The value of sn_num_olss_minus1    shall be in the range of 0 to TotalNumOlss−1, inclusive.    sn_ols_idx_delta_minus1[i] is used to derive the variable    NestingOlsIdx[i] that specifies the OLS index of the i-th OLS to    which the scalable-nested SEI messages apply when sn_ols_flag is    equal to 1. The value of sn_ols_idx_delta_minus1[i] shall be in the    range of 0 to TotalNumOlss−2, inclusive, inclusive.    The variable NestingOlsIdx[i] is derived as follows:

if( i = = 0 )  NestingOlsIdx[ i ] = sn_ols_idx_delta_minus1[ i ] (D.4)else  NestingOlsIdx[ i ] = NestingOlsIdx[ i − 1 ] + sn_ols_idx_delta_minus1[ i ] + 1sn_all_layers_flag equal to 1 specifies that the scalable-nested SEImessages apply to all layers that have nuh_layer_id greater than orequal to the nuh_layer_id of the current SEI NAL unit.sn_all_layers_flag equal to 0 specifies that the scalable-nested SEImessages may or may not apply to all layers that have nuh layer idgreater than or equal to the nuh_layer_id of the current SEI NAL unit.sn_num_layers_minus1 plus 1 specifies the number of layers to which thescalable-nested SEI messages apply. The value of sn_num_layers_minus1shall be in the range of 0 to vps_max_layers_minus1 —GeneralLayerIdx[nuh_layer_id], inclusive, where nuh_layer_id is thenuh_layer_id of the current SEI NAL unit.sn_layer_id[i] specifies the nuh layer id value of the i-th layer towhich the scalable-nested SEI messages apply when sn_all_layers_flag isequal to 0. The value of sn_layer_id[i] shall be greater thannuh_layer_id, where nuh_layer_id is the nuh_layer_id of the current SEINAL unit.When sn_ols_flag is equal to 0, the variable NestingNumLayers,specifying the nubmer of layer to which the scalable-nested SEI messagesapply, and the list NestingLayerId[i] for i in the range of 0 toNestingNumLayers−1, inclusive, specifying the list of nuh layer id valueof the layers to which the scalable-nested SEI messages apply, arederived as follows, where nuh_layer_id is the nuh_layer_id of thecurrent SEI NAL unit:

if( sn_all_layers_flag ) {  NestingNumLayers = vps_max_layers_minus1 + 1− GeneralLayerIdx[ nuh_layer_id ]  for( i = 0; i < NestingNumLayers; i++)   NestingLayerId[ i ] = vps_layer_id[ GeneralLayerIdx[  nuh_layer_id ] + i ]  (D.5) } else {  NestingNumLayers =sn_num_layers_minus1 + 1  for( i = 0; i < NestingNumLayers; i ++)  NestingLayerId[ i ] = ( i = = 0 ) ? nuh_layer_id : sn_layer_id[ i ] }

sn_num_subpics_minus1 plus 1 specifies the number of subpictures

[[to which the scalable-nested SEI messages apply]]. The value ofsn_num_subpics_minus1 shall be less than or equal to the value ofsps_num_subpics_minus1 in the SPSs referred to by the pictures in the

[[CLVS]].

[[sn_subpic_id_len_minus1plus 1 specifies the number of bits used torepresent the syntax element sn_subpic_id[i]. The value ofsn_subpic_id_len_minus1 shall be in the range of 0 to 15, inclusive.

-   It is a requirement of bitstream conformance that the value of    sn_subpic_id_len_minus1 shall be the same for all scalable nesting    SEI messages that are present in a CLVS.]]

sn_subpic_idx[i] [[indicates]]

the i-th subpicture [[ID associated with the scalable-nested SEImessages]]

[[The length of the sn_subpic_id[i] syntax element issn_subpic_id_len_minus1+1 bits.]]

sn_num_seis_minus1 plus 1 specifies the number of scalable-nested SEImessages. The value of sn_num_seis_minus1 shall be in the range of 0 to63, inclusive.sn_zero_bit shall be equal to 0.

FIG. 5 is a block diagram showing an example video processing system1900 in which various embodiments disclosed herein may be implemented.Various embodiments may include some or all of the components of thesystem 1900. The system 1900 may include input 1902 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8- or 10-bit multi-component pixel values, or may be in acompressed or encoded format. The input 1902 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as Wi-Fi orcellular interfaces.

The system 1900 may include a coding component 1904 that may implementthe various coding or encoding methods described in the presentdisclosure. The coding component 1904 may reduce the average bitrate ofvideo from the input 1902 to the output of the coding component 1904 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 1904 may be eitherstored, or transmitted via a communication connected, as represented bythe component 1906. The stored or communicated bitstream (or coded)representation of the video received at the input 1902 may be used bythe component 1908 for generating pixel values or displayable video thatis sent to a display interface 1910. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or DisplayPort, and so on. Examples of storageinterfaces include serial advanced technology attachment (SATA),peripheral component interface (PCI), integrated drive electronics (IDE)interface, and the like. The embodiments described in the presentdisclosure may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

FIG. 6 is a block diagram of a video processing apparatus 3600. Theapparatus 3600 may be used to implement one or more of the methodsdescribed herein. The apparatus 3600 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 3600 may include one or more processors 3602, one or morememories 3604 and video processing hardware 3606. The processor(s) 3602may be configured to implement one or more methods described in thepresent disclosure. The memory (memories) 3604 may be used for storingdata and code used for implementing the methods and embodimentsdescribed herein. The video processing hardware 3606 may be used toimplement, in hardware circuitry, some embodiments described in thepresent disclosure.

FIG. 8 is a block diagram that illustrates an example video codingsystem 100 that may utilize the embodiments of this disclosure.

As shown in FIG. 8 , video coding system 100 may include a source device110 and a destination device 120. Source device 110 generates encodedvideo data which may be referred to as a video encoding device.Destination device 120 may decode the encoded video data generated bysource device 110 which may be referred to as a video decoding device.

Source device 110 may include a video source 112, a video encoder 114,and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, aninterface to receive video data from a video content provider, and/or acomputer graphics system for generating video data, or a combination ofsuch sources. The video data may comprise one or more pictures. Videoencoder 114 encodes the video data from video source 112 to generate abitstream. The bitstream may include a sequence of bits that form acoded representation of the video data. The bitstream may include codedpictures and associated data. The coded picture is a codedrepresentation of a picture. The associated data may include sequenceparameter sets, picture parameter sets, and other syntax structures. I/Ointerface 116 may include a modulator/demodulator (modem) and/or atransmitter. The encoded video data may be transmitted directly todestination device 120 via I/O interface 116 through network 130 a. Theencoded video data may also be stored onto a storage medium/server 130 bfor access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface126 may acquire encoded video data from the source device 110 or thestorage medium/ server 130 b. Video decoder 124 may decode the encodedvideo data. Display device 122 may display the decoded video data to auser. Display device 122 may be integrated with the destination device120, or may be external to destination device 120 which be configured tointerface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a videocompression standard, such as the HEVC standard, VVC standard, and othercurrent and/or further standards.

FIG. 9 is a block diagram illustrating an example of video encoder 200,which may be video encoder 114 in the system 100 illustrated in FIG. 8 .

Video encoder 200 may be configured to perform any or all of theembodiments of this disclosure. In the example of FIG. 9 , video encoder200 includes a plurality of functional components. The embodimentsdescribed in this disclosure may be shared among the various componentsof video encoder 200. In some examples, a processor may be configured toperform any or all of the embodiments described in this disclosure.

The functional components of video encoder 200 may include a partitionunit 201, a prediction unit 202 which may include a mode select unit203, a motion estimation unit 204, a motion compensation unit 205, andan intra prediction unit 206; a residual generation unit 207; atransform unit 208; a quantization unit 209; an inverse quantizationunit 210; an inverse transform unit 211; a reconstruction unit 212; abuffer 213; and an entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, ordifferent functional components. In an example, prediction unit 202 mayinclude an intra block copy (IBC) unit. The IBC unit may performprediction in an IBC mode in which at least one reference picture is apicture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 andmotion compensation unit 205 may be highly integrated, but arerepresented in the example of FIG. 9 separately for purposes ofexplanation.

Partition unit 201 may partition a picture into one or more videoblocks. Video encoder 200 and video decoder 300 may support variousvideo block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter,e.g., based on error results, and provide the resulting intra- orinter-coded block to a residual generation unit 207 to generate residualblock data and to a reconstruction unit 212 to reconstruct the encodedblock for use as a reference picture. In some examples, mode select unit203 may select a combination of intra and inter prediction (CIIP) modein which the prediction is based on an inter prediction signal and anintra prediction signal. Mode select unit 203 may also select aresolution for a motion vector (e.g., a sub-pixel or integer pixelprecision) for the block in the case of inter prediction.

To perform inter prediction on a current video block, motion estimationunit 204 may generate motion information for the current video block bycomparing one or more reference frames from buffer 213 to the currentvideo block. Motion compensation unit 205 may determine a predictedvideo block for the current video block based on the motion informationand decoded samples of pictures from buffer 213 other than the pictureassociated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may performdifferent operations for a current video block, for example, dependingon whether the current video block is in an I slice, a P slice, or a Bslice.

In some examples, motion estimation unit 204 may perform uni-directionalprediction for the current video block, and motion estimation unit 204may search reference pictures of list 0 or list 1 for a reference videoblock for the current video block. Motion estimation unit 204 may thengenerate a reference index that indicates the reference picture in list0 or list 1 that contains the reference video block and a motion vectorthat indicates a spatial displacement between the current video blockand the reference video block. Motion estimation unit 204 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the current video block. Motioncompensation unit 205 may generate the predicted video block of thecurrent block based on the reference video block indicated by the motioninformation of the current video block.

In other examples, motion estimation unit 204 may perform bi-directionalprediction for the current video block, motion estimation unit 204 maysearch the reference pictures in list 0 for a reference video block forthe current video block and may also search the reference pictures inlist 1 for another reference video block for the current video block.Motion estimation unit 204 may then generate reference indexes thatindicate the reference pictures in list 0 and list 1 containing thereference video blocks and motion vectors that indicate spatialdisplacements between the reference video blocks and the current videoblock. Motion estimation unit 204 may output the reference indexes andthe motion vectors of the current video block as the motion informationof the current video block. Motion compensation unit 205 may generatethe predicted video block of the current video block based on thereference video blocks indicated by the motion information of thecurrent video block.

In some examples, motion estimation unit 204 may output a full set ofmotion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may not output a full setof motion information for the current video. Rather, motion estimationunit 204 may signal the motion information of the current video blockwith reference to the motion information of another video block. Forexample, motion estimation unit 204 may determine that the motioninformation of the current video block is sufficiently similar to themotion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntaxstructure associated with the current video block, a value thatindicates to the video decoder 300 that the current video block has thesame motion information as the another video block.

In another example, motion estimation unit 204 may identify, in a syntaxstructure associated with the current video block, another video blockand a motion vector difference (MVD). The motion vector differenceindicates a difference between the motion vector of the current videoblock and the motion vector of the indicated video block. The videodecoder 300 may use the motion vector of the indicated video block andthe motion vector difference to determine the motion vector of thecurrent video block.

As discussed above, video encoder 200 may predictively signal the motionvector. Two examples of predictive signalling techniques that may beimplemented by video encoder 200 include advanced motion vectorprediction (AMVP) and merge mode signalling.

Intra prediction unit 206 may perform intra prediction on the currentvideo block. When intra prediction unit 206 performs intra prediction onthe current video block, intra prediction unit 206 may generateprediction data for the current video block based on decoded samples ofother video blocks in the same picture. The prediction data for thecurrent video block may include a predicted video block and varioussyntax elements.

Residual generation unit 207 may generate residual data for the currentvideo block by subtracting (e.g., indicated by the minus sign) thepredicted video block(s) of the current video block from the currentvideo block. The residual data of the current video block may includeresidual video blocks that correspond to different sample components ofthe samples in the current video block.

In other examples, there may be no residual data for the current videoblock for the current video block, for example in a skip mode, andresidual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transformcoefficient video blocks for the current video block by applying one ormore transforms to a residual video block associated with the currentvideo block.

After transform processing unit 208 generates a transform coefficientvideo block associated with the current video block, quantization unit209 may quantize the transform coefficient video block associated withthe current video block based on one or more quantization parameter (QP)values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may applyinverse quantization and inverse transforms to the transform coefficientvideo block, respectively, to reconstruct a residual video block fromthe transform coefficient video block. Reconstruction unit 212 may addthe reconstructed residual video block to corresponding samples from oneor more predicted video blocks generated by the prediction unit 202 toproduce a reconstructed video block associated with the current blockfor storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loopfiltering operation may be performed reduce video blocking artifacts inthe video block.

Entropy encoding unit 214 may receive data from other functionalcomponents of the video encoder 200. When entropy encoding unit 214receives the data, entropy encoding unit 214 may perform one or moreentropy encoding operations to generate entropy encoded data and outputa bitstream that includes the entropy encoded data.

FIG. 10 is a block diagram illustrating an example of video decoder 300which may be video decoder 124 in the system 100 illustrated in FIG. 8 .

The video decoder 300 may be configured to perform any or all of theembodiments of this disclosure. In the example of FIG. 10 , the videodecoder 300 includes a plurality of functional components. Theembodiments described in this disclosure may be shared among the variouscomponents of the video decoder 300. In some examples, a processor maybe configured to perform any or all of the embodiments described in thisdisclosure.

In the example of FIG. 10 , video decoder 300 includes an entropydecoding unit 301, a motion compensation unit 302, an intra predictionunit 303, an inverse quantization unit 304, an inverse transform unit305, a reconstruction unit 306, and a buffer 307. Video decoder 300 may,in some examples, perform a decoding pass generally reciprocal to theencoding pass described with respect to video encoder 200 (FIG. 9 ).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encodedbitstream may include entropy coded video data (e.g., encoded blocks ofvideo data). Entropy decoding unit 301 may decode the entropy codedvideo data, and from the entropy decoded video data, motion compensationunit 302 may determine motion information including motion vectors,motion vector precision, reference picture list indexes, and othermotion information. Motion compensation unit 302 may, for example,determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used with sub-pixelprecision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used byvideo encoder 200 during encoding of the video block to calculateinterpolated values for sub-integer pixels of a reference block. Motioncompensation unit 302 may determine the interpolation filters used byvideo encoder 200 according to received syntax information and use theinterpolation filters to produce predictive blocks.

Motion compensation unit 302 may use some of the syntax information todetermine sizes of blocks used to encode frame(s) and/or slice(s) of theencoded video sequence, partition information that describes how eachmacroblock of a picture of the encoded video sequence is partitioned,modes indicating how each partition is encoded, one or more referenceframes (and reference frame lists) for each inter-encoded block, andother information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for examplereceived in the bitstream to form a prediction block from spatiallyadjacent blocks. Inverse quantization unit 304 inverse quantizes, i.e.,de-quantizes, the quantized video block coefficients provided in thebitstream and decoded by entropy decoding unit 301. Inverse transformunit 305 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with thecorresponding prediction blocks generated by motion compensation unit302 or intra-prediction unit 303 to form decoded blocks. If desired, adeblocking filter may also be applied to filter the decoded blocks inorder to remove blockiness artifacts. The decoded video blocks are thenstored in buffer 307, which provides reference blocks for subsequentmotion compensation/intra prediction and also produces decoded video forpresentation on a display device.

A listing of solutions preferred by some embodiments is provided next.

The following solutions show example embodiments discussed in theprevious section (e.g., all items).

1. A video processing method, comprising: performing a conversionbetween a video comprising one or more subpictures or one or moresubpicture sequences and a coded representation of the video, whereinthe coded representation conforms to a format rule specifying whether orhow scalable-nested supplemental enhancement information (SEI) isincluded in the coded representation.

The following solutions show example embodiments discussed in theprevious section (e.g., item 1).

2. The method of solution 1, wherein the format rule specifies that thecoded representation uses subpicture indices to associate subpictures tocorresponding scalable-nested SEI information.

The following solutions show example embodiments discussed in theprevious section (e.g., item 2).

3. The method of any of solutions 1-2, wherein the format rule disallowsuse of filter payload SEI messages in a scalable-nested manner.

The following solutions show example embodiments discussed in theprevious section (e.g., item 3).

4. The method of any of solutions 1-3, wherein the format rule specifiesthat, for a scalable-nested SEI message that includes one or moresubpicture level information SEI messages, a flag is included in thecoded representation for indicating a presence of the one or moresubpicture level information SEI messages.

The following solutions show example embodiments discussed in theprevious section (e.g., item 4).

5. The method of any of solutions 1-4, wherein the format rule disablesinclusion of nested SEI messages of a payload of a certain type in ascalable SEI message containing a message of the certain type.

The following solutions show example embodiments discussed in theprevious section (e.g., item 5).

6. The method of any of solutions 1-5, wherein the format rule specifiesthat an SEI message that is not of a filler payload type or a decodedpicture hash type is required to have a specific network abstractionlayer unit type.

The following solutions show example embodiments discussed in theprevious section (e.g., item 6).

7. The method of any of solutions 1-6, wherein the format rule specifiesthat an SEI message that is of a decoded picture hash type is requiredto have a specific network abstraction layer unit type.

The following solutions show example embodiments discussed in theprevious section (e.g., item 7).

8. The method of any of solutions 1-7, wherein the format rule specifiesthat the syntax elements specify information about the subpictures ofthe layers that have multiple subpictures per picture.

9. The method of any of solutions 1 to 8, wherein the conversioncomprises encoding the video into the coded representation.

10. The method of any of solutions 1 to 8, wherein the conversioncomprises decoding the coded representation to generate pixel values ofthe video.

11. A video decoding apparatus comprising a processor configured toimplement a method recited in one or more of solutions 1 to 10.

12. A video encoding apparatus comprising a processor configured toimplement a method recited in one or more of solutions 1 to 10.

13. A computer program product having computer code stored thereon, thecode, when executed by a processor, causes the processor to implement amethod recited in any of solutions 1 to 10.

14. A method, apparatus or system described in the present disclosure.

In the solutions described herein, an encoder may conform to the formatrule by producing a coded representation according to the format rule.In the solutions described herein, a decoder may use the format rule toparse syntax elements in the coded representation with the knowledge ofpresence and absence of syntax elements according to the format rule toproduce decoded video.

FIG. 13 is a flowchart for an example method 1300 of processing videodata. Operation 1302 includes performing a conversion between a videocomprising one or more subpictures and a bitstream of the video, whereinone or more supplemental enhancement information messages that havefiller payloads are processed during the conversion according to aformat rule, and wherein the format rule disallows the one or moresupplemental enhancement information messages having filler payloads tobe in a scalable nesting supplemental enhancement information message.

In some embodiments of method 1300, the one or more supplementalenhancement information messages that have filler payloads include apayload type that has a value equal to 3. In some embodiments of method1300, the format rule disallows one or more second supplementalenhancement information messages having scalable nesting to be in ascalable nesting supplemental enhancement information message.

FIG. 14 is a flowchart for an example method 1400 of processing videodata. Operation 1402 includes performing a conversion between a videoand a bitstream of the video, wherein one or more syntax elements areprocessed during the conversion according to a format rule, and whereinthe format rule specifies that the one or more syntax elements are usedfor indicating subpicture information for layers of the video that havepictures with multiple subpictures.

In some embodiments of method 1400, the one or more syntax elementsinclude a first syntax element, and wherein a value of the first syntaxelement plus 1 specifies a number of subpictures in the pictures withmultiple subpictures. In some embodiments of method 1400, the value ofthe first syntax element is less than or equal to a value of a secondsyntax element in a sequence parameter set referred to by pictures inmultiple subpicture layers. In some embodiments of method 1400, the oneor more syntax elements include a third syntax element, and wherein thethird syntax element indicates a subpicture index of an i-th subpicturein each picture in the pictures with multiple subpictures. In someembodiments of method 1400, the first syntax element is labeled assn_num_subpics_minus1 . In some embodiments of method 1400, the thirdsyntax element is labeled as sn_subpic_idx[ i ].

FIG. 15 is a flowchart for an example method 1500 of processing videodata. Operation 1502 includes performing a conversion between a videocomprising a plurality of subpictures and a bitstream of the video,wherein a scalable-nested supplemental enhancement information messageis processed during the conversion according to a format rule, andwherein the format rule specifies use of one or more subpicture indicesto associate one or more subpictures to the scalable-nested supplementalenhancement information message.

In some embodiments of method 1500, the format rule disallows use of oneor more subpicture identifiers to associate the one or more subpicturesto the scalable-nested supplemental enhancement information message. Insome embodiments of method 1500, the format rule replaces a first syntaxelement with a second syntax element in the scalable-nested supplementalenhancement information message, the format rule removes a third syntaxelement from the scalable-nested supplemental enhancement informationmessage, the first syntax element indicates the a subpicture identifierof an i-th subpicture in each picture in one or more video layers, thesecond syntax element indicates a subpicture index of an i-th subpicturein each picture in the one or more video layers, and the third syntaxelement plus 1 specifies a number of bits used to represent the firstsyntax element.

FIG. 16 is a flowchart for an example method 1600 of processing videodata. Operation 1602 includes performing a conversion between a videocomprising one or more subpictures and a bitstream of the videoaccording to a format rule, wherein the format rule specifies that afirst syntax element in a scalable nesting supplemental enhancementinformation message in the bitstream is set to a particular value inresponse to the scalable nesting supplemental enhancement informationmessage including one or more subpicture level information supplementalenhancement information messages, and wherein the particular value ofthe first syntax element indicates that the scalable nestingsupplemental enhancement information message includes one or morescalable-nested supplemental enhancement information messages that applyto a specific output video layer set.

In some embodiments of method 1600, the format rule that specifies thata value of a second syntax element in the bitstream is equal to 0 inresponse to the scalable nesting supplemental enhancement informationmessage including the one or more subpicture level informationsupplemental enhancement information messages, and the value of thesecond syntax element being equal to 0 specifies that the scalablenesting supplemental enhancement information message includes the one ormore scalable-nested supplemental enhancement information messages thatapply to one or more output video layer sets or one or more video layersapply to all subpictures of the one or more output video layer sets orthe one or more video layers. In some embodiments of method 1600, theformat rule specifies that a payload type of the one or morescalable-nested supplemental enhancement information messages in thescalable nesting supplemental enhancement information message is 203,and a payload type of 203 for a supplemental enhancement informationmessage indicates that the supplemental enhancement information messageis a subpicture level information supplemental enhancement informationmessage. In some embodiments of method 1600, the particular value of thefirst syntax element is equal to 1.

FIG. 17 is a flowchart for an example method 1700 of processing videodata. Operation 1702 includes performing a conversion between a videocomprising a plurality of subpictures and a bitstream of the video,wherein the conversion is according to a format rule that specifies thata scalable nesting supplemental enhancement information message isdisallowed from including a first supplemental enhancement informationmessage of a first payload type and a second supplemental enhancementinformation message of a second payload type.

In some embodiments of method 1700, the first payload type includes apayload type of a buffering period supplemental enhancement informationmessage. In some embodiments of method 1700, the first payload typeincludes a payload type of a picture timing supplemental enhancementinformation message. In some embodiments of method 1700, the firstpayload type includes a payload type of a decoding unit informationsupplemental enhancement information message. In some embodiments ofmethod 1700, the first payload type includes a payload type of asubpicture level information supplemental enhancement informationmessage. In some embodiments of method 1700, the second payload typeincludes a payload type that is not one of the following: (i) thepayload type of a buffering period supplemental enhancement informationmessage, (ii) the payload type of a picture timing supplementalenhancement information message, (iii) the payload type of a decodingunit information supplemental enhancement information message, and (iv)the payload type of a subpicture level information supplementalenhancement information message.

FIG. 18 is a flowchart for an example method 1800 of processing videodata. Operation 1802 includes performing a conversion between a videoand a bitstream of the video, wherein the conversion is performedaccording to a format rule that specifies that a supplementalenhancement information network abstraction layer unit includes anetwork abstraction layer unit type equal to a prefix supplementalenhancement information network abstraction layer unit type in responseto the supplemental enhancement information network abstraction layerunit including a scalable nesting supplemental enhancement informationmessage that includes a supplemental enhancement information message notassociated with a particular payload type.

In some embodiments of method 1800, the network abstraction layer unittype is equal to PREFIX_SEI_NUT.

FIG. 19 is a flowchart for an example method 1900 of processing videodata. Operation 1902 includes performing a conversion between a videoand a bitstream of the video, wherein the conversion is performedaccording to a format rule that specifies that a supplementalenhancement information network abstraction layer unit includes anetwork abstraction layer unit type equal to a suffix supplementalenhancement information network abstraction layer unit type in responseto the supplemental enhancement information network abstraction layerunit including a scalable nesting supplemental enhancement informationmessage that includes a supplemental enhancement information messageassociated with a particular payload type.

In some embodiments of method 1900, the network abstraction layer unittype is equal to SUFFIX_SEI_NUT.

In some embodiments of method(s) 1800-1900, the particular payload typeis a payload type of a decoded picture harsh supplemental enhancementinformation message. In some embodiments of method(s) 1800-1900, theparticular payload type is associated with a value equal to 132.

In some embodiments of method(s) 1300-1900, performing the conversioncomprises encoding the video into the bitstream. In some embodiments ofmethod(s) 1300-1900, performing the conversion comprises generating thebitstream from the video, and the method further comprises storing thebitstream in a non-transitory computer-readable recording medium. Insome embodiments of method(s) 1300-1900, performing the conversioncomprises decoding the video from the bitstream. In some embodiments, avideo decoding apparatus comprising a processor configured to implementmethod(s) 1300-1900 or an embodiment thereof. In some embodiments, avideo encoding apparatus comprising a processor configured to implementmethod(s) 1300-1900 or an embodiment thereof. In some embodiments, acomputer program product having computer instructions stored thereon,the instructions, when executed by a processor, causes the processor toimplement method(s) 1300-1900 or an embodiment thereof. In someembodiments, a non-transitory computer-readable storage medium thatstores a bitstream generated according to method(s) 1300-1900 or anembodiment thereof. In some embodiments, a non-transitorycomputer-readable storage medium storing instructions that cause aprocessor to implement method(s) 1300-1900 or an embodiment thereof. Insome embodiments, a method of bitstream generation, comprising:generating a bitstream of a video according to method(s) 1300-1900 or anembodiment thereof, and storing the bitstream on a computer-readableprogram medium. In some embodiments, a method, an apparatus, a bitstreamgenerated according to a disclosed method or a system described in thepresent disclosure.

Some embodiments of the present disclosure include making a decision ordetermination to enable a video processing tool or mode. In an example,when the video processing tool or mode is enabled, the encoder will useor implement the tool or mode in the processing of a block of video, butmay not necessarily modify the resulting bitstream based on the usage ofthe tool or mode. That is, a conversion from the block of video to thebitstream representation of the video will use the video processing toolor mode when it is enabled based on the decision or determination. Inanother example, when the video processing tool or mode is enabled, thedecoder will process the bitstream with the knowledge that the bitstreamhas been modified based on the video processing tool or mode. That is, aconversion from the bitstream representation of the video to the blockof video will be performed using the video processing tool or mode thatwas enabled based on the decision or determination.

Some embodiments of the present disclosure include making a decision ordetermination to disable a video processing tool or mode. In an example,when the video processing tool or mode is disabled, the encoder will notuse the tool or mode in the conversion of the block of video to thebitstream representation of the video. In another example, when thevideo processing tool or mode is disabled, the decoder will process thebitstream with the knowledge that the bitstream has not been modifiedusing the video processing tool or mode that was disabled based on thedecision or determination.

In the present disclosure, the term “video processing” may refer tovideo encoding, video decoding, video compression or videodecompression. For example, video compression algorithms may be appliedduring conversion from pixel representation of a video to acorresponding bitstream representation or vice versa. The bitstreamrepresentation of a current video block may, for example, correspond tobits that are either co-located or spread in different places within thebitstream, as is defined by the syntax. For example, a macroblock may beencoded in terms of transformed and coded error residual values and alsousing bits in headers and other fields in the bitstream. Furthermore,during conversion, a decoder may parse a bitstream with the knowledgethat some fields may be present, or absent, based on the determination,as is described in the above solutions. Similarly, an encoder maydetermine that certain syntax fields are or are not to be included andgenerate the coded representation accordingly by including or excludingthe syntax fields from the coded representation.

The disclosed and other solutions, examples, embodiments, modules andthe functional operations described in this disclosure can beimplemented in digital electronic circuitry, or in computer software,firmware, or hardware, including the structures disclosed in thisdisclosure and their structural equivalents, or in combinations of oneor more of them. The disclosed and other embodiments can be implementedas one or more computer program products, i.e., one or more modules ofcomputer program instructions encoded on a computer readable medium forexecution by, or to control the operation of, data processing apparatus.The computer readable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this disclosure can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., a field-programmable gate array (FPGA) or anapplication-specific integrated circuit (ASIC).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., erasable programmable read-onlymemory (EPROM), electronically erasable programmable read-only memory(EEPROM), and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto optical disks; and compact disc,read-only memory (CD-ROM) and digital versatile disc, read-only memory(DVD-ROM) disks. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

While the present disclosure contains many specifics, these should notbe construed as limitations on the scope of any subject matter or ofwhat may be claimed, but rather as descriptions of features that may bespecific to particular embodiments of the present disclosure. Certainfeatures that are described in the present disclosure in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in the present disclosure should not be understoodas requiring such separation in all embodiments.

Only a few embodiments and examples are described and other embodiments,enhancements and variations can be made based on what is described andillustrated in the present disclosure.

What is claimed is:
 1. A method of processing video data, comprising:performing a conversion between a video and a bitstream of the video,wherein, during the conversion, one or more syntax elements included ina scalable nesting supplemental enhancement information (SEI) messageare according to a format rule, and wherein the format rule specifiesthat the one or more syntax elements are used for indicating subpictureinformation for multiple subpicture layers, which are layers of thevideo that have pictures with multiple subpictures.
 2. The method ofclaim 1, wherein the one or more syntax elements include a first syntaxelement, and wherein a value of the first syntax element plus 1specifies a number of subpictures in each picture of the multiplesubpicture layers.
 3. The method of claim 2, wherein the value of thefirst syntax element is less than or equal to a value of a second syntaxelement in a sequence parameter set referred to by pictures in themultiple subpicture layers, and wherein the value of the second syntaxelement plus 1 specifies a number of subpictures in each picturereferring to the sequence parameter set.
 4. The method of claim 2,wherein the first syntax element is labeled as sn_num_subpics_minus1. 5.The method of claim 1, wherein the one or more syntax elements include athird syntax element, and wherein the third syntax element indicates asubpicture identifier of an i-th subpicture in each picture in themultiple subpicture layers.
 6. The method of claim 1, whereinscalable-nested SEI messages are allowed to apply to a single subpicturein each picture in layers that are not in the multiple subpicturelayers, but are among layers in specific output layer sets (OLSs) towhich the scalable-nested SEI messages apply, or among specific layersto which the scalable-nested SEI messages apply.
 7. The method of claim1, wherein the format rule disallows one or more SEI messages havingfiller payload to be in the scalable nesting SEI message.
 8. The methodof claim 1, wherein the one or more SEI messages have a payload typevalue equal to
 3. 9. The method of claim 1, wherein the format ruledisallows one or more second SEI messages having scalable nesting thathave a payload type value equal to 133 to be in the scalable nesting SEImessage.
 10. The method of claim 1, wherein performing the conversioncomprises encoding the video into the bitstream.
 11. The method of claim1, wherein performing the conversion comprises decoding the video fromthe bitstream.
 12. An apparatus for processing video data comprising aprocessor and a non-transitory memory with instructions thereon, whereinthe instructions upon execution by the processor, cause the processorto: perform a conversion between a video and a bitstream of the video,wherein, during the conversion, one or more syntax elements included ina scalable nesting supplemental enhancement information (SEI) messageare according to a format rule, and wherein the format rule specifiesthat the one or more syntax elements are used for indicating subpictureinformation for multiple subpicture layers, which are layers of thevideo that have pictures with multiple subpictures.
 13. The apparatus ofclaim 12, wherein the one or more syntax elements include a first syntaxelement, and wherein a value of the first syntax element plus 1specifies a number of subpictures in each picture of the multiplesubpicture layers, wherein the first syntax element is labeled assn_num_subpics_minus1, and wherein the value of the first syntax elementis less than or equal to a value of a second syntax element in asequence parameter set referred to by pictures in the multiplesubpicture layers, and wherein the value of the second syntax elementplus 1 specifies a number of subpictures in each picture referring tothe sequence parameter set.
 14. The apparatus of claim 12, wherein theone or more syntax elements include a third syntax element, and whereinthe third syntax element indicates a subpicture identifier of an i-thsubpicture in each picture in the multiple subpicture layers.
 15. Theapparatus of claim 12, wherein scalable-nested SEI messages are allowedto apply to a single subpicture in each picture in layers that are notin the multiple subpicture layers, but are among layers in specificoutput layer sets (OLSs) to which the scalable-nested SEI messagesapply, or among specific layers to which the scalable-nested SEImessages apply.
 16. The apparatus of claim 12, wherein the format ruledisallows one or more SEI messages having filler payload to be in thescalable nesting SEI message, wherein the one or more SEI messages havea payload type value equal to 3, and wherein the format rule disallowsone or more second SEI messages having scalable nesting that have apayload type value equal to 133 to be in the scalable nesting SEImessage.
 17. A non-transitory computer-readable storage medium storinginstructions that cause a processor to: perform a conversion between avideo and a bitstream of the video, wherein, during the conversion, oneor more syntax elements included in a scalable nesting supplementalenhancement information (SEI) message are according to a format rule,and wherein the format rule specifies that the one or more syntaxelements are used for indicating subpicture information for multiplesubpicture layers, which are layers of the video that have pictures withmultiple subpictures.
 18. The non-transitory computer-readable storagemedium of claim 17, wherein the one or more syntax elements include afirst syntax element, and wherein a value of the first syntax elementplus 1 specifies a number of subpictures in each picture of the multiplesubpicture layers, wherein the first syntax element is labeled assn_num_subpics_minus1, wherein the value of the first syntax element isless than or equal to a value of a second syntax element in a sequenceparameter set referred to by pictures in the multiple subpicture layers,and wherein the value of the second syntax element plus 1 specifies anumber of subpictures in each picture referring to the sequenceparameter set, wherein the one or more syntax elements include a thirdsyntax element, and wherein the third syntax element indicates asubpicture identifier of an i-th subpicture in each picture in themultiple subpicture layers, wherein scalable-nested SEI messages areallowed to apply to a single subpicture in each picture in layers thatare not in the multiple subpicture layers, but are among layers inspecific output layer sets (OLSs) to which the scalable-nested SEImessages apply, or among specific layers to which the scalable-nestedSEI messages apply, wherein the format rule disallows one or more SEImessages having filler payload to be in the scalable nesting SEImessage, wherein the one or more SEI messages have a payload type valueequal to 3, and wherein the format rule disallows one or more second SEImessages having scalable nesting that have a payload type value equal to133 to be in the scalable nesting SEI message.
 19. A non-transitorycomputer-readable recording medium storing a bitstream of a video whichis generated by a method performed by a video processing apparatus,wherein the method comprises: generating the bitstream of the video,wherein, during the generating, one or more syntax elements included ina scalable nesting supplemental enhancement information (SEI) messageare according to a format rule, and wherein the format rule specifiesthat the one or more syntax elements are used for indicating subpictureinformation for multiple subpicture layers, which are layers of thevideo that have pictures with multiple subpictures.
 20. Thenon-transitory computer-readable recording medium of claim 19, whereinthe one or more syntax elements include a first syntax element, andwherein a value of the first syntax element plus 1 specifies a number ofsubpictures in each picture of the multiple subpicture layers, whereinthe first syntax element is labeled as sn_num_subpics_minus1, whereinthe value of the first syntax element is less than or equal to a valueof a second syntax element in a sequence parameter set referred to bypictures in the multiple subpicture layers, and wherein the value of thesecond syntax element plus 1 specifies a number of subpictures in eachpicture referring to the sequence parameter set, wherein the one or moresyntax elements include a third syntax element, and wherein the thirdsyntax element indicates a subpicture identifier of an i-th subpicturein each picture in the multiple subpicture layers, whereinscalable-nested SEI messages are allowed to apply to a single subpicturein each picture in layers that are not in the multiple subpicturelayers, but are among layers in specific output layer sets (OLSs) towhich the scalable-nested SEI messages apply, or among specific layersto which the scalable-nested SEI messages apply, wherein the format ruledisallows one or more SEI messages having filler payload to be in thescalable nesting SEI message, wherein the one or more SEI messages havea payload type value equal to 3, and wherein the format rule disallowsone or more second SEI messages having scalable nesting that have apayload type value equal to 133 to be in the scalable nesting SEImessage.